When i draw with the brush and then press E to switch to the eraser, it doesn't work, and I need to draw again and press E again for it to work. sometimes I need to press it 8 times, other times it doesn't work at all. Can this be fixed? step backwards also has the same issue

No, other people are not seeing such a problem using shortcuts (though some are reporting problems new to MacOS 10.10). It could be a third party plugin, an HTML panel, a utility program or another application on your system messing with the key events.